Stomatal density and stomatal length in relation to photosynthetic and transpirational behaviour of paddy rice varieties and their yield, and yield components.

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Fifteen varieties of paddy rice (Oryza sativa L. subsp. japonica and subsp. indica) including different plant types were chosen from current and past recommended varieties in Ehime prefecture and from super high yield varieties. Photosynthetic and transpiration rates of flag leaves were measured hourly for several days from heading through ripening periods using a portable gas analyzer (Analytical Development Co. Ltd., England). Stomatal density( <mm^(-2)> ) and stomatal length ( <mu> ) were examined with enamel repricas of abaxial and adaxial sides of the flag leaf. The leaf area, yield and yield components were also investigated.1. Varietal difference of net photosynthetic rate was clearly indicated on a fine day, although the difference disappeared when clouds arouse around at noon even in a few hours.2. Many varieties showed their maximum photosynthesis at 10-12 a.m. In some varieties, however, the maximum occurred at 8-9 a.m. and 2 p.m. independently of solar radiation intensities … More .3. A high correlation coefficient r= <0.783^(***)> was observed between varietal photosynthetic rates and varietal stomatal conductances on a fine day.4. Relations between stomatal conductance and stomatal density X stomatal length were investigated in each hour. Strong correlations were generally recognized, but they disappeared at hours when solar radiation exhibited very high intensities. The author considered that the potential stomatal conductance of varieties was essentially related with their stomatal density X stomatal length. Therefore, the correlation was weakened by stomatal closure of varieties which developed water stress.5. Super high yield Korean varieties had very many stomata,ranging from 5.6 to 7.1 millions per flag leaf in number. This number was 2-2.5 times as large as that of Japanese common varieties. Total stomatal length (= number of stomata X stomatal length) of the flag leaf was severely correlated with number of grains per head (r= <0.784^(***)> ), and with yield (r= <0.694^(**)> ). Less